1. Field of the Invention
The present invention relates to semiconductor devices and systems.
2. Description of the Related Art
A technique that connects a termination resistor to the end of a transmission line in a memory module and thereby reduces reflections of signals therein is disclosed in Patent Literature 1 (JP2002-23901A, Publication).
In recent years, memory devices provided with various functions besides an information storage function have been released. For example, a DDR4 DRAM (Double Data Rate 4 Dynamic Random Access Memory), which is a memory module, is newly provided with an alert signal output function that outputs errors such as a CRC (Cyclic Redundancy Check) error and a parity check error to the outside of the DRAM. Such a DDR4 DRAM is provided with an alert pin that is an output terminal that outputs an alert signal.
FIG. 1 is a schematic diagram showing an example of connections of a memory module substrate on which a plurality of DRAMs each having an alert signal output function are mounted.
As shown in FIG. 1, in memory module 1000 on which DRAMs 2000-1 to 2000-9 are mounted, a signal line for a CA (Command and Address) signal and a CTRL (Control) signal that are input from the outside of memory module 1000 are connected in series to input terminals 1002 of DRAMs 2000-1 to 2000-9. This signal line is also connected to termination resistor 3000 preceded by DRAM 2000-9 that is the farthest from input terminal 1002 of memory module 1000. On the other hand, a signal line for alert signals that DRAMs 2000-1 to 2000-9 output so as to notify the remote controller that an error occurs is connected in series to alert terminals of DRAMs 2000-1 to 2000-9. Thus, the alert signals that are input from DRAMs 2000-1 to 2000-9 are output from output terminal 1001 of memory module 1000 to the memory controller.
However, if the foregoing signal line is long, a problem in which alert signals reflect on the signal line will occur. For example, in the connections shown in FIG. 1, if an alert signal is output from the alert terminal of DRAM 2000-9, the alert signal propagates not only in the direction of output terminal 1001, but also in the direction of DRAM 2000-8. As a result, the alert signal that propagates in the direction of DRAM 2000-8 reflects at DRAM 2000-1 and then propagates in the direction of output terminal 1001 of memory module 1000. Thus, the alert signals that are output from output terminal 1001 get distorted. Moreover, SODIMMs (Small Outline Dual In-Line Memory Modules) have various system structures such as 1 DPC (DIMM Per Channel) and 2DPC and thereby reflections of alert signals and DC Low levels become complicated.